21380881 has 2 divisors, whose sum is σ = 21380882. Its totient is φ = 21380880.

The previous prime is 21380867. The next prime is 21380893. The reversal of 21380881 is 18808312.

It is a strong prime.

It can be written as a sum of positive squares in only one way, i.e., 21344400 + 36481 = 4620^2 + 191^2 .

It is a cyclic number.

It is not a de Polignac number, because 21380881 - 2⁷ = 21380753 is a prime.

It is a super-2 number, since 2×21380881² = 914284144672322, which contains 22 as substring.

It is not a weakly prime, because it can be changed into another prime (21380851) by changing a digit.

It is a polite number, since it can be written as a sum of consecutive naturals, namely, 10690440 + 10690441.

It is an arithmetic number, because the mean of its divisors is an integer number (10690441).

Almost surely, 2^21380881 is an apocalyptic number.

It is an amenable number.

21380881 is a deficient number, since it is larger than the sum of its proper divisors (1).

21380881 is an equidigital number, since it uses as much as digits as its factorization.

21380881 is an evil number, because the sum of its binary digits is even.

The product of its (nonzero) digits is 3072, while the sum is 31.

The square root of 21380881 is about 4623.9464746037. The cubic root of 21380881 is about 277.5504050419.

The spelling of 21380881 in words is "twenty-one million, three hundred eighty thousand, eight hundred eighty-one".